1. Field of the Invention
The present invention relates to a lighting unit for a vehicle headlamp and, more particularly, to a projector type lighting unit constructed to form a low-beam light distribution pattern.
2. Background Art
Commonly, the projector type lighting unit used in the vehicle headlamp is constructed such that a projection lens is arranged on an optical axis extending in the longitudinal direction of a vehicle, then a light source is arranged on the rear side of a rear side focal point, and then a light from the light source is reflected by a reflector toward the optical axis.
When the low-beam light distribution pattern is formed by the projector type lighting unit, a part of the reflected light from the reflector is shielded by a shade that is arranged to pass its upper end edge near the rear side focal point of the projection lens, and thus a predetermined cut-off line is formed on an upper end portion of the low-beam light distribution pattern.
In “Patent Document 1”, the projector type lighting unit employing a light emitting element arranged to direct upward as the light source is set forth.
In the projector type lighting unit in “Patent Document 1”, a mirror member whose upward reflecting surface for reflecting a part of the reflected light from the reflector to the upward side is provided between the reflector and the projection lens and also whose front end edge is formed to pass through the rear side focal point of the projection lens is provided. Thus, a part of the reflected light from the reflector is reflected to the upward side by the mirror member such that the low-beam light distribution pattern having a cut-off line as a reversed projection image of the front end edge of the upward reflecting surface on its upper end portion is formed.
[Patent Document 1] JP-A-2003-317515
When the projector type lighting unit equipped with such mirror member in “Patent Document 1” is employed, the low-beam light distribution pattern having the clear cut-off line on its upper end portion can be formed, while enhancing a utility factor of a luminous flux of the light from the light emitting element.
However, the projector type lighting unit is constructed such that a light source image formed on a rear side focal plane of the projection lens is projected forward by the reflected light from the reflector. Therefore, as the lighting unit in “Patent Document 1”, even when the lighting unit is constructed to reflect a part of the reflected light from the reflector to the upward side by the mirror member, neither a brightness of a hot zone (i.e., high luminous intensity area) of the low-beam light distribution pattern formed in this manner can be increased largely, nor a highest luminous intensity position can be set in a position in vicinity of the cut-off line. As a result, such a problem existed that a visibility of the far area on the road surface in front of the vehicle cannot sufficiently enhanced.